Lens driver

ABSTRACT

In a lens driving apparatus according to the present invention, as shown in FIG. 1, a positioning dowel  2   b  which rotatably supports a shaft of a driving member  9  so as not to have a backlash is formed in a lens holding frame  2,  a rack part  9   f  and a coil spring mounting dowel  9   h  are formed in the driving member  9,  a coil spring  11  is mounted on the coil spring mounting dowel  9   h  of the driving member  9,  and the rack part  9   f  of the driving member  9  is pressed against a feed screw  7   a  of a motor for driving  6  by using the positioning dowel  2   b  of the lens holding frame  2  as a rotation fulcrum, as well as the lens driving apparatus has an elastic rotating force in a direction along which the lens holding frame  2  is made to abut on a second guide pole  4,  and further a moment in a direction along which the lens holding frame  2  is pressed against the second guide pole  4  by the self-weight of the lens holding frame  2  including the lens  1  is also added.  
     According to the lens driving apparatus so constructed, a photographed video does not vibrate due to a vibration by the motor for driving, thereby realizing the lens driving apparatus which faithfully transmits a feed displacement by the motor for driving as the feed displacement of the lens and has a stable driving performance.

TECHNICAL FIELD

[0001] The present invention relates to a lens driving apparatus which performs focus adjustment (hereinafter abbreviated as focusing) by performing lens position adjustment of a master lens when a subject is photographed using a video camera or the like and, more particularly, to a lens driving apparatus which can prevent defocusing during zooming operation at manual focusing or defocusing of a photographed image which is involved by a difference between positions at photographing.

BACKGROUND ART

[0002] Conventionally, a focusing operation of a lens driving apparatus included in a video camera or the like, which is disclosed in Japanese Published Patent Application No. Hei. 6-308361, has been known, and this will be described with reference to figures hereinafter. FIG. 8 is a perspective view illustrating a main portion of a conventional lens driving apparatus, FIG. 9 is an expanded cross sectional view illustrating a relationship between a feed screw and a first arm of a driving member in the lens driving apparatus shown in FIG. 8, FIG. 10 is an expanded cross sectional view illustrating a relationship between the feed screw and a second arm or the driving member in the lens driving apparatus shown in FIG. 8, FIG. 11 is an expanded cross sectional view illustrating a combination relationship between the driving member and a lens holding frame in the lens driving apparatus shown in FIG. 8, FIG. 12 is an expanded cross sectional view illustrating a combination and protection relationship between the driving member and the lens holding frame in the lens driving apparatus shown in FIG. 8, FIG. 13 is a cross sectional section of a main section illustrating the conventional lens driving apparatus when the apparatus is faced in the horizontal direction to perform photographing, and FIG. 14 is a cross sectional view of a main section illustrating the conventional lens driving apparatus at tilt-photographing.

[0003] A structure of the conventional lens driving apparatus will be described hereinafter. In FIG. 8, a lens 1 which performs focusing of a subject is fixed to a lens holding frame 2 made of a resin, by a means such as heat-staking, and is held by a first guide pole 3 and a second guide pole 4 which are arranged in, a fixed body tube (not shown) so as to be slidable in the direction of a lens optical axis 5. Further, there is provided a groove 2 a for connection on the upper part of the lens holding frame 2, which groove connects a driving member 9 to the lens holding frame 2, and further, there is provided a feed screw 7 a in a driving axis 7 of a motor for driving 6 which motor is attached to the fixed body tube, and the driving member 9 made of a resin is slidably held by a third guide pole 10 arranged at a motor mounting body 8 in parallel with the driving axis 7. Furthermore, this driving member 9 is provided with a notch nut 9 a which is threadedly engaged with the feed screw 7 a as shown in FIG. 9, and a first arm 9 b having spring characteristics for supporting the feed screw 7 a by sandwiching the screw 7 a is formed.

[0004] On the other hand, a second arm 9 d is formed in the driving member 9 as shown in FIG. 10, and a gap between the second arm 9 d and a thread part of the feed screw 7 a is constructed so as to have a smaller gap size than a screw thread height size of the notch nut 9 a. Further, there is provided an edge portion 9 c having enough rigidity to slidably move the lens holding frame 2 and having spring characteristics, in a connected portion of the driving member 9 with the lens holding frame 2 as shown in FIG. 11, and this edge portion 9 c is inserted into the groove 2 a in an arrow direction, thereby constructing a backlash-free connection in the direction of the lens optical axis 5. Further, there is provided a stopper edge portion 9 e which does not abut against the groove 2 a in the connected portion of the driving member 9 as shown in FIG. 12, so that the edge portion 9 c having the spring characteristics is not curved to a spring limit due to shock.

[0005] In the conventional lens driving apparatus so constructed, the operation thereof will be described hereinafter. The feed screw 7 a formed in the driving axis 7 is inserted in the notch nut 9 a of the driving member 9 so as to be pressured and energized by the first arm 9 b having the spring characteristics. In this case, since the driving member 9 is slid by the third guide pole 10 to move in the direction of the lens optical axis 5 when the motor for driving 6 rotates, the lens holding frame 2 connected to the driving member 9 is also slid by the first guide pole 3 and the second guide pole 4 in accordance with a rotation of the motor for driving 6 to move in the direction of the lens optical axis 5, thereby to obtain focusing by the lens 1.

[0006] However, in this construction, the driving member 9 supports the feed screw 7 a by sandwiching it through the notch nut 9 a and the first arm 9 b. Therefore, when the feed screw 7 a vibrates at the rotation of the motor for driving 6, this vibration is directly transmitted to the driving member 9, thereby vibrating around the third guide pole 10. Since the driving member 9 and the lens holding frame 2 are connected to each other in the direction of the lens optical axis 5 by the edge portion 9 c having the spring characteristics without backlash, the vibration is transmitted to the lens holding frame 2 without being completely absorbed in the edge portion 9 c having the spring characteristics, and therefore, the lens vibrates, whereby, when focusing is performed, an image shakes so that a photographed video becomes hard to view.

[0007] Further, even when a tilt-photography is performed by a video camera which is provided with this lens driving apparatus, there is a problem as follows. That is, when a focusing operation is performed while photographing is performed in a state where the video camera is horizontal, the lens holding frame 2 which holds the lens 1 is slid by the first guide pole 3 and the second guide pole 4, further, the driving member 9 is slid by the third guide pole 10, and the lens holding frame 2 and the driving member 9, having the respective clearances d, horizontally move in the direction of the lens optical axis 5 to perform focusing as shown in FIG. 13.

[0008] When photographing is performed in a slightly tilted state from this state, as shown in FIG. 14, the edge portion 9 c having the spring characteristics cannot absorb a slope of the lens holding frame 2, and therefore, the lens holding frame 2 tilts in a self-weight direction of the lens 1 shown by an arrow W3, by a smaller clearance of a clearance D2 held by the first guide pole 3 and the lens holding frame 2 or a clearance D3 held by the third guide pole 10 and the driving member 9, thereby accordingly generating a tilt in the lens 1 and then a single blur phenomenon of the photographed video.

[0009] The present invention is made to solve these problems, and has for its object to provide a lens driving apparatus which faithfully transmits a feed displacement by the motor for driving as the feed displacement of the lens and has a stable driving performance, as well as in which apparatus the photographed video does not vibrate due Lo a vibration by the motor for driving.

DISCLOSURE OF THE INVENTION

[0010] In a lens driving apparatus according to the present invention (claim 1) having a lens holding frame which holds a lens and is guided by a first guide pole and a second guide pole to slidably move in the lens optical axis direction, a driving shaft having a feed screw which is rotated and driven by a motor, and a driving member which has a rack threadedly engaged with the feed screw of the driving shaft at one end and is engaged with the lens holding frame at the other end, wherein the driving member is mounted rotatably to a positioning dowel which is provided in the lens holding frame and extends in the lens optical axis direction by a positioning hole provided in the driving member, and a spring member, which presses the rack of the driving member against the driving shaft as well as provides an elastic rotating force in a direction along which the lens holding frame Was pressed against the second guide pole, is provided between the lens holding frame and the driving member, and a moment in a direction along which the lens holding frame is pressed against the second guide pole by a self-weight of the lens holding frame is added in the elastic rotating force of the spring member. Thereby, it can be avoided that a photographed video vibrates due to a random vibration produced by a rotation of the motor for driving, and further a feed displacement by the motor for driving can be faithfully transmitted as the feed displacement of the lens.

[0011] According to the tens driving apparatus of the present invention (claim 2), in the lens driving apparatus of claim 1, the driving member is made of a resin material, and two leg parts capable of elastic deformation and parallel with each other, which are respectively provided with positioning holes at their tips, are formed integrally with the driving member, and the positioning dowel formed in the lens holding frame has a taper shape the diameter of which becomes smaller toward a tip, and the diameter of a bottom part of the positioning dowel is constructed so as to be larger than the diameter of the positioning hole of the driving member. Thereby, the feed displacement by the motor for driving at photographing can be faithfully transmitted as the feed displacement of the lens, and a continually stable driving performance of the lens can be guaranteed.

[0012] According to the lens driving apparatus of the present invention (claim 3), in the lens driving apparatus of claim 2, a stopper which restricts deformation and omission of the driving member is formed integrally with the driving member and the lens holding frame. Thereby, when an external force acts on the lens holding frame due to a fall, shock, or the like, the driving member can be prevented from being separated away from the lens holding frame.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is an exploded perspective view of a main portion according to an embodiment of a lens driving apparatus of the present invention.

[0014]FIG. 2 is a side view illustrating a state where a driving member and a coil spring are attached to a lens holding frame of the lens driving apparatus shown in FIG. 1.

[0015]FIG. 3 is a vector diagram illustrating directions of forces to act between a position where the lens holding frame and the coil spring are abutted and a position where the lens holding frame and a second guide pole are abutted in the lens driving apparatus shown in FIG. 1.

[0016]FIG. 4 is a cross sectional view of a main section illustrating a state where a leg part of the driving member is attached to a positioning dowel of the lens holding frame in the lens driving apparatus shown in FIG. 1.

[0017]FIG. 5 is a cross sectional view of a main section illustrating a stopper of the driving member in the lens driving apparatus shown in FIG. 1.

[0018]FIG. 6 is a cross sectional view of a main section illustrating a state where an external force acts on the lens holding frame to create displacement in the lens driving apparatus shown in FIG. 1.

[0019]FIG. 7 is a cross sectional view of a main section illustrating a state where the lens driving apparatus shown in FIG. 1 is tilted upward.

[0020]FIG. 8 is a perspective view of a main section in a conventional lens driving apparatus.

[0021]FIG. 9 is a partially cross sectional view illustrating an engagement of a first arm having spring characteristics of the driving member and a feed screw in the conventional lens driving apparatus.

[0022]FIG. 10 is a partially cross sectional view illustrating an engagement of a second arm of the driving member and the feed screw in the conventional lens driving apparatus.

[0023]FIG. 11 is a partially cross sectional view illustrating a state where an edge portion having spring characteristics of the driving member and the lens holding frame engage with each other in the conventional lens driving apparatus.

[0024]FIG. 12 is a partially cross sectional view illustrating a state where a stopper edge portion of the driving member is inserted in a groove for a joint of the lens holding frame in the conventional lens driving apparatus.

[0025]FIG. 13 is a cross sectional view of a main section when the conventional lens driving apparatus is faced in a horizontal direction to perform photographing.

[0026]FIG. 14 is a cross sectional view of a main section illustrating a state where the conventional lens driving apparatus is tilted upward.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to figures. Further, the same numerals are given to the same parts as the above-described conventional example, and the detailed description thereof will be omitted.

[0028]FIG. 1 is an exploded perspective view of a main portion of a lens driving apparatus according to an embodiment of the present invention, FIG. 2 is a side view illustrating a state where a driving member and a coil spring are attached to a lens holding frame in the lens driving apparatus shown in FIG. 1, FIG. 3 is a vector diagram illustrating directions of forces which act between a position where the lens holding frame and the coil spring are abutted and a position where the lens holding frame and a second guide pole are abutted in the lens driving apparatus shown in FIG. 1, FIG. 4 is a cross sectional view of a main section illustrating a state where a leg part of the driving member is attached to a positioning dowel of the lens holding frame in the lens driving apparatus shown in FIG. 1, FIG. 5 is a cross sectional view of a main section illustrating a stopper of the driving member in the lens driving apparatus shown in FIG. 1, FIG. 6 is a cross sectional view of a main section illustrating a state where an external force acts on the lens holding frame to create displacement in the lens driving apparatus shown in FIG. 1, and FIG. 7 is a cross sectional view of a main section illustrating a state where the lens driving apparatus shown in FIG. 1 is tilted upward.

[0029] In FIGS. 1 and 2, numeral 1 denotes a lens, and numeral 2 denotes a lens holding frame made of a resin, for holding the lens 1. The lens holding frame 2 is held by a first guide pole 3 and a second guide pole 4, and has a constant clearance D1 positioned in the second guide pole 4 to be guided, and slidably moves in the direction of a lens optical axis 5. Numeral 9 denotes a driving member which connects the lens holding frame 2 with a feed screw 7 a formed in a driving axis 7 of a motor for driving 6. On the driving member 9, the following components are integrally formed: a leg part 9 j capable of elastic deformation, which part is composed of two plates having spring characteristics and extending in parallel with each other, a mounting dowel 9 h which mounts a coil spring 11, a first groove 9 g against which an end portion of the coil spring 11 abuts, and a rack part 9 which is pressured and energized by the feed screw 7 a and makes the driving member 9 itself move in the direction of the lens optical axis 5 together with a rotation of the feed screw 7 a. Further, the leg part 9 j is provided with a positioning hole 9 i which engages with the positioning dowel 2 b formed in the lens holding frame 2 and makes the leg part 9 j and the lens holding frame 2 rotatable to each other.

[0030] Further, the coil spring 11 is engaged with the mounting dowel 9 h, and the first end portion 11 a and the second end portion 11 b abut against the first groove 9 g formed in the driving member 9 and the second groove 2 e formed in the lens holding frame 2, respectively, and the rack part 9 f abuts against the feed screw 7 a by a reaction force of the coil spring 11, as well as the lens holding frame 2 is constructed so as to rotate in a counterclockwise direction by using the first guide pole 3 as a rotation fulcrum shaft. Further, the lens holding frame 2 is provided with an engaging part 2 c integrally formed with this lens holding frame 2 as a stopper.

[0031] In a lens driving apparatus so constructed, as shown in FIG. 2, a force always acts on a C-point of the lens holding frame 2 which has a constant clearance D1 in the second guide pole 4 to be slidably and movably held in a counterclockwise direction shown by an arrow, by the reaction force of the coil spring 11, and this will be described in details with reference to the vector view shown in FIG. 3.

[0032] In FIG. 3, A shows a center of the first guide pole 3 shown in FIG. 2, B shows a contact point between the second groove 2 e and the coil spring 11, and C shows a contact point between the second guide pole 4 and the lens holding frame 2.

[0033] When a vertical direction component of an elastic rotating force generated by the coil spring 11 to a line segment which links A to B is FB, a rotation moment is generated in the counterclockwise direction by taking the center A of the first guide pole 3 as reference. Accordingly, when a component which acts in a vertical direction to a line segment which links the A-point to the C-point is FC in the C-point, a force in a direction of FC=FB×AB/AC always acts. Further, the moment in a direction along which the lens holding frame 2 press-contacts with the second guide pole 4 by a self-weight W1 of the lens holding frame 2 including the lens 1 is added in the elastic rotating force.

[0034] Next, as shown in FIG. 4, the positioning dowel 2 b having a taper-like projecting shape the diameter of which becomes smaller toward a tip, which dowel is formed integrally with the lens holding frame 2, is attached to the leg part 9 j of the driving member 9 in a state where the positioning dowel 2 b is elastically supported by being sandwiched, and, as shown in FIG. 2, the driving member 9 is rotated by the coil spring 11 in a clockwise direction, whereby the rack part 9 f formed in this driving member 9 is threadedly engaged with the feed screw 7 a. Further, the positioning hole 9 i formed in the leg part 9 j has a taper-like projecting shape the diameter of which becomes smaller toward a tip such that the driving member 9 easily rotates, and is in linear contact so as not to generate a backlash due to a clearance between the positioning hole 9 i and the positioning dowel 2 b of the lens holding frame 2, whereby the rotating friction resistance is small. Further, as shown in FIG. 5, a projection 9 k is provided at a tip of the driving member 9, and an engaging part 2 c is integrally formed on the lens holding frame 2 in a position which is apart from a tip of the projection 9 k by clearance, so as to constitute the stopper by engaging with the projection 9 k.

[0035] In this way, the driving member 9 and the lens holding frame 2 engage with each other, whereby, as shown in FIG. 6, when a force in a direction shown by an arrow F acts on the lens holding frame 2 due to a fall, shock, or the like, lift is produced against the positioning dowel 9 b in the leg part 9 j. However, at this time, the projection 9 k integrally formed at a tip of the driving member 9 abuts against the engaging part 2 c beforehand, so that the leg part 9 j is not separated away from the positioning dowel 2 b.

[0036] In the lens driving apparatus so constructed, an operation thereof will be described hereinafter. When the video camera is trained on a given subject, the lens driving apparatus built in the video camera operates to perform focusing on the subject, and the lens 1 in this lens driving apparatus is moved to the focusing position, by an automatic focusing control circuit not shown. At this focusing operation, the lens driving apparatus shown in FIGS. 1 and 2 operates so that the motor for driving 6 rotates, the driving member 9 pressed against the feed screw 7 a by the coil spring 11 moves in the direction of the lens optical axis 5 in accordance with the rotation of the motor for driving 6, and the lens holding frame 2 connected to the driving member 9 is also guided by the first guide pole 3 and the second guide pole 4 in accordance with the rotation of the motor for driving 6 to slidably move in the direction of the lens optical axis 5, thereby obtaining focusing by using the lens 1.

[0037] At this time, although the feed screw 7 a vibrates by a rotational vibration of the motor for driving 6, a vibration of the feed screw 7 a is transmitted to the driving member 9, because the rack part 9 f of the driving member 9 is always pressed against the feed screw 7 a. However, since the coil spring 11 which provides the elastic rotating force is disposed between the driving member 9 and the lens holding frame 2, and further a moment in a direction along which the lens holding frame 2 is pressed against the second guide pole 4 by the self-weight of the lens holding frame 2 including the lens 1 is also added in the elastic rotating force, the vibration which is produced in the lens holding frame 2 is absorbed.

[0038] Next, a description will be given of a case where the lens driving apparatus according to this embodiment is tilted upward with reference to FIG. 7. As shown in FIG. 7, the leg part 9 j of the driving member 9 elastically supports the positioning dowel 2 b having a taper-like projecting shape, which dowel is formed in the lens holding frame 2, by sandwiching the dowel 2 b. In addition, the positioning hole 9 i formed in the leg part 9 j has a taper-like projecting shape and is in linear contact so as not to generate a backlash due to a clearance between the positioning hole 9 i and the positioning dowel 2 b of the lens holding frame 2. Further, the driving member 9 is pressed against the feed screw 7 a by the above-described action of the coil spring 11, and a moment in a direction along which the lens holding frame 2 press-contacts with the second guide pole 4 is provided. Therefore, such a conventional phenomenon that focusing is off by that the lens 1 is tilted due to a difference between positions is removed. In addition, the driving member 9 can faithfully transmit the feed displacement of the feed screw 7 a to the lens holding frame 2 as the feed displacement, and the lens 1 is guided by the first guide pole 3 and the second guide pole 4, thereby moving the lens 1 in the direction of the lens optical axis 5. Further, W2 denotes a self-weight in the direction of the lens optical axis 5.

[0039] Further, while an example in which the leg part 9 j is integrally formed in the driving member 9 is described in this embodiment, this leg part 9 j may be a different member that is separated from the driving member 9. Further, while the coil spring 11 is described as a different member from the driving member 9, the driving member 9 may be provided with a member having spring characteristics as an integrated part.

[0040] As described above, according to this embodiment, the vibration of the motor for driving 6 is absorbed by the coil spring 11 which is disposed between the driving member 9 and the lens holding frame 2, and by the press from the lens holding frame 2 against the second guide pole 4 due to the self-weight of the lens holding frame 2 including the lens 1. Therefore, the vibration of the lens 1 can be removed, thereby removing the vibration of the photographed video. Further, the positioning dowel 2 b provided in the lens holding frame 2 is constructed so as to be elastically supported by being sandwiched by the positioning dowel 9 i provided in the leg part 9 j of the driving member 9, thereby removing an occurrence of the backlash due to a clearance between the members, faithfully transmitting the feed displacement by the motor for driving 6 at photographing as the feed displacement of the lens 1, and guaranteeing the continually stable driving performance of the lens 1.

[0041] Industrial Availability

[0042] As described above, the lens driving apparatus according to the present invention relates to a lens driving apparatus which performs focus adjustment (focusing) by performing lens position adjustment of a master lens when a subject is photographed by using a video camera or the like, and, more particularly, the lens driving apparatus can prevent defocusing during a zooming operation at manual focusing or defocusing of a photographed image which is involved by a difference between positions at photographing. 

1. A lens driving apparatus having a lens holding frame which holds a lens and is guided by a first guide pole and a second guide pole to slidably move in the lens optical axis direction, a driving shaft having a feed screw which is rotated and driven by a motor, and a driving member which has a rack threadedly engaged with the feed screw of the driving shaft at one end and is engaged with the lens holding frame at the other end, wherein the driving member is mounted rotatably to a positioning dowel which is provided in the lens holding frame and extends in the lens optical axis direction by a positioning hole provided in the driving member, and a spring member, which presses the rack of the driving member against -.he driving shaft as well as provides an elastic rotating force in a direction along which the lens holding frame is pressed against the second guide pole, is provided between the lens holding frame and the driving member, and a moment in a direction along which the lens holding frame is pressed against the second guide pole by a self-weight of the lens holding frame is added in the elastic rotating force of the spring member.
 2. The lens driving apparatus of claim 1 wherein the driving member is made of a resin material, and two leg parts capable of elastic deformation and parallel with each other, which are respectively provided with positioning holes at their tips, are formed integrally with the driving member, and the positioning dowel formed in the lens holding frame has a taper shape the diameter of which becomes smaller toward a tip, and the diameter of a bottom part of the positioning dowel is constructed so as to be larger than the diameter of the positioning hole of the driving member.
 3. The lens driving apparatus of claim 2 wherein a stopper which restricts deformation and omission of the driving member is formed integrally with the driving member and the lens holding frame. 